High power beam tube having depressed potential collector containing field-shaping probe

Claim 1

In a high power electron beam tube having a depressed potential collector: thermionic cathode emitter means having a concave emitting surface for thermionically emitting electrons; centrally apertured accelerating anode means spaced from said emitter means and shaped for drawing a convergent stream of electrons through the central aperture of said anode in a substantially non-intercepting manner to form a laminar flow electron beam of generally uniform current density taken transversely across the beam path; collector means disposed at the terminal end of the beam path for collecting the electron beam, said collector operating at a depressed potential in respect to said anode means and having an electrically conductive cavity with a constricted mouth for receiving said beam in said cavity and for inhibiting egress of secondary and reflected electrons from said cavity, collector focusing means disposed at the mouth of said collector, and tapered conductive probe means disposed axially within said collector cavity, said probe having a terminating free end portion disposed approximately at the mouth of said collector cavity, said free end portion having a half-cone angle of less than 20* and a free end tip portion which has a transverse cross-sectional area for interception of beam current, said tip portion occupying less than 1 percent of the area of said constricted mouth of said collector cavity, said collector focusing means and said probe means being formed and arranged for shaping the equally potentials of the electron decelerating field at the mouth of said collector to maintain a generally laminar electron flow of uniform cross density taken transversely across the decelerated beam at the mouth of said collector cavity in the presence of regions of space charge depression within said collector cavity, whereby electrons will not be reflected out of said cavity and hence the efficiency of said tube will be substantially increased.